First let's tackle the power supply. This was a bloody nightmare to get right. What I built is NOT what I intended to build, but I'm documenting what I ended up with (even if I don't fully understand it).
My first design and prototype used an LM317T voltage regulator which was supplying a sweet 6 volts to the circuit. But just as I set out to build the actual circuit, I started to have second thoughts as I wondered whether I should add a heatsink for the LM317T. Even though I did the maths and figured out that I wouldn't need a heatsink, I ultimately dropped the LM317T. And here in lies my biggest mistake... I changed the design mid-flight! Boy, did I regret that later on.
R2 and R3 are simply there to divide the voltage (a technique I explained in the Buffer post). The TL061 requires power to be supplied to Vcc+ to get it to work AND to the input audio signal (via R2 and R5 in my circuit). The datasheet instructs you to have less voltage on the audio input than the Vcc+ and that the audio input voltage must not exceed 4.5v. It seems that everybody simply halves the 9v Vcc+ voltage, so this is what I did too.
I can't explain R1. It is a bit of residual DNA from multiple hack and slashes I undertook while troubleshooting problems. In my mind it isn't adding anything at all to this circuit, but it's there in my working pedal and so I'm showing it to you. If you build this circuit, experiment with taking it out and let me know what you discover. I think this might have been me trying to reduce the voltage even further across the circuit, but then I hit problems.
These two same capacitors are in the circuit for the Buffer Pedal and they serve the same purpose here. Go check that article out for more detail. I didn't have them with my original LM317T design, but they are definitely required for the Booster circuit as it stands now; They remove a mains hum that my circuit was suffering from in testing. And a pretty good job they do too!
Here I'm highlighting the DC isolation capacitors. AGAIN, this is exactly what we talked about with the Buffer Pedal. Isn't it nice when that happens! The values I'm using here are tailored for the TL061.
The combination of C5 & C6 are simply me getting around the problem where I didn't have the right capacitor size to allow me to use just the one. From my scribbled notes I think that the original MXR calls for a single 15uf capacitor here.
Finally, I'm highlighting the input and output stages.
I explained a lot of this in the Buffer post, so this time, I'll just call out a couple of things specific to this circuit:
R5 and R7 are as per the MXR. They're far bigger than I would like, but it works so don't knock it.
R12 and R13 are NOT as per the MXR. This isn't a typo. You'll see that I swapped the two resistors around as I tuned this for the best audio I could get.
Look at this bloody rat's nest!
I managed to get it all into a box, but it's a bit of a tight squeeze!
If I've done this right, you can see a couple of examples of the pedal in action in this video. First up is my homemade Sharkfin travel uke. It works well, but I think that the Buffer pedal might have the edge for this particular piezo. I don't play anything too exciting here, but you do get a feel for the range of the pedal. I can't see me using the "squeal like a pig" mode, but never say never ;-)
Next up is my trusty guitar. I've never used this through an amp because it sounds so bad amped up. Well, listen to it through the Booster pedal... amazing! Unfortunately the recording doesn't quite do the sound justice. I found that the pedal worked best on the guitar with a low to mid boost. Adding reverb made it peachy ;-)
I wonder what a true electric might sound like... an experiment for another day.
Here's a photo of the boxed pedal sat next to its brother. I haven't tried chaining them... another experiment for another day.
Finally, I leave you with a recommendation. See this "Classic Ragtime Guitar Solos" by Stefan Grossman. I picked it up a couple of weekends ago. It is brilliant. I buy books like this all of the time from random charity shops. Rarely do I actually learn anything from them. Song one in this book is an old Tom Turpin song called The Bowery Bucks arranged for guitar by Dick Fegy. The original was played on piano. I see that a scan of the sheet music is available from the Library of Congress if you can read music.
I've been learning the tune in-between everything else going on and I love it. It's the tune I murder in the video above. One day I will play the whole thing for you fumble-free... perhaps ;-)
That's your lot!